Methods of preparing clusterboron

ABSTRACT

New methods are provided for synthesis of ClusterBoron® (B 18 H 22 ). Preferred methods of the invention include generation of the conjugate acid of B 20 H 18   2−  and degradation of the acid in solution to produce B 18 H 22  in high yields and high purity. The invention further provides isotopically enriched boranes, particularly isotopically enriched  10 B 18 H 22  and  11 B 18 H 22 .

RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.12/741,200, filed May 3, 2010, which is a 35 U.S.C. §371 U.S. nationalentry of International Application PCT/US2008/012473 (WO 2009/058408)having an International filing date of Nov. 3, 2008 which claims thebenefit of U.S. provisional application No. 61/001,633 filed Nov. 2,2007, all of which are incorporated by reference herein in theirentirety.

BACKGROUND

The present application claims the benefit of U.S. provisionalapplication No. 61/001633 filed Nov. 2, 2007, which is incorporated byreference herein in its entirety.

1. Field of the Invention

The invention provides methods for synthesizing B₁₈H₂₂ as a mixture ofsyn and anti isomers, commonly marketed as ClusterBoron. The inventionfurther provides isotopically enriched B₁₈H₂₂ prepared by theaforementioned methods. In particular, the invention relates thepreparation of natural abundance B₁₈H₂₂, ¹⁰B-enriched B₁₈H₂₂ and¹¹B-enriched B₁₈H₂₂.

2. Background

Large boron hydride compounds have become important feed stocks forboron doped P-type impurity regions in semiconductor manufacture. Moreparticularly, high molecular weight boron hydride compounds, e.g., boronhydride compounds comprising at least a five (5) boron atom cluster, arepreferred boron atom feed stocks for molecular boron implantation.

An important aspect of modern semiconductor technology is the continuousdevelopment of smaller and faster devices. This process is calledscaling. Scaling is driven by continuous advances in lithographicprocess methods, allowing the definition of smaller and smaller featuresin the semiconductor substrate which contains the integrated circuits. Agenerally accepted scaling theory has been developed to guide chipmanufacturers in the appropriate resize of all aspects of thesemiconductor device design at the same time, i.e., at each technologyor scaling node. The greatest impact of scaling on ion implantationprocesses is the scaling of junction depths, which requires increasinglyshallow junctions as the device dimensions are decreased. Thisrequirement for increasingly shallow junctions as integrated circuittechnology scales translates into the following requirement: ionimplantation energies must be reduced with each scaling step. Theextremely shallow junctions called for by modern, sub-0.13 microndevices are termed “Ultra-Shallow Junctions” or USJs.

Methods of manufacturing boron doped P-type junctions have been hamperedby difficulty in controlling the ion-implantation process using boron.The single boron atom, being light (MW=10.8), can penetrate too deeplyinto a silicon substrate and diffuse throughout the substrate latticerapidly during annealing or other elevated temperature processes.

Boron clusters or cages, e.g., boranes have been investigated as a feedstock for delivering molecular boron species to a semiconductorsubstrate with reduced penetration. See PCT/US03/20197.

Large boron hydride compounds, that is boron compounds having between 5and about 100 boron atoms are preferred for use in molecular ionimplantation methods for delivering boron atoms to a semiconductorsubstrate. Typically, there may be isomers of the boron hydride compoundthat exist. That is, boron hydrides with the same number of boron andhydrogen atoms that possess different chemical properties, e.g.structural isomers or stereoisomers. In addition, two or morestructurally related boron hydride compounds having the same number ofboron atoms but different numbers of hydrogen atoms have been isolatedfor various sized boron clusters. For example, pentaborane(9) andpentaborane(11) have chemical formulas of B₅H₉ and B₅H₁₁ respectively.Such compounds are frequently calssified as closo (B_(n)H_(n)),nido(B_(n)H_(n+2)), arachno (B_(n)H_(n+4)), hypho (B_(n)H_(n+6)),conjuncto (B_(n)H_(n+) 8), and the like. Thus, different boron hydridespecies, including isomers and compounds containing various amounts ofhydrogen, are frequently known for boron hydrides having n boron atoms.Jemmis, et al. have provided a review of various macropolyhedral boranesand known compounds having n boron atoms and various amounts ofhydrogen.^(1,2)

Mixtures of isomers and mixtures of n-boron atom containing boronhydrides are suitable for use in the implantation methods discussed. Themolecular ions generated by the ionization process of boron hydridemixtures will have uniform and narrow weight distributions.

Current synthetic technologies for the preparation of large boronhydride molecules, e.g., boron hydride molecules with more than 12 boronatoms, are often plagued by complicated synthetic processes, lowisolated yields, and/or inconsistent reproducibility.

Although there are several synthetic routes reported in the literaturefor the preparation of B₁₈H₂₂ as a mixture of isomers, they are lengthy,often result in notably low yields, are unreliable and have safetyissues associated with the synthesis.

It thus would be desirable to have new methods for preparation ofB₁₈H₂₂.

DESCRIPTION OF THE INVENTION

We have now discovered new methods for the preparation ofoctadecaborane, B₁₈H₂₂. The invention is particularly useful for facilesynthesis and purification of large quantities of B₁₈H₂₂. The presentinvention also relates to isotopically-enriched B₁₈H₂₂. Whereas, bydefinition, enriched means the modification of the boron isotopesnatural abundance. Depending on source natural abundance of the ¹⁰Bisotope ranges from 19.10% to 20.31% and natural abundance of the ¹¹Bisotope ranges from 80.90% to 79.69%.

A typical B₁₈H₂₂molecular ion beam contains a wide range of ion massesdue to a varying number of hydrogen losses from the molecular ion aswell as the varying mass due to the two naturally occurring isotopes. Asmass selection is possible in an implanter device used in semiconductormanufacture, use of isotopically enriched boron in B₁₈H₂₂ can greatlyreduce the spread of masses, thereby providing an increased beam currentof the desired implantation species. Thus, ¹¹B and ¹⁰Bisotopically-enriched B₁₈H₂₂ is also of great interest.

In one aspect, the invention provides methods of synthesizingoctadecaborane (B₁₈H₂₂), the method comprising (a) contacting the saltof borane anion B₂₀H₁₈ ²⁻ with an acid to produce H₂B₂₀H₁₈xH₂O; andthen preferably (b)removing water from the reaction vessel in thepresence of a B₁₈H₂₂ solubilizing solvent that remains essentiallychemically inert in the system.

In certain aspects the invention provides synthesizing B₁₈H₂₂ by methodscomprising the steps of:

(a) contacting the borane anion B₂₀H₁₈ ²⁻ in solvent with an acidicion-exchange resin to produce a solution of H₂B₂₀H₁₈xH₂O;(b) concentrating the mixture comprising H₂B₂₀H₁₈xH₂O;(c) removing water from the reaction vessel in the presence of a B₁₈H₂₂solubilizing solvent that remains essentially chemically inert in thesystem;(d) separating insoluble byproducts from the reaction mixture through(i) filtration and/or(ii) concentration of reaction solvent, dissolution of B₁₈H₂₂ intoaliphatic solvent and filtration of byproducts;(e) isolation of B₁₈H₂₂ through removal of solvent.

Such a preferred process is represented schematically in the flow chart(FIG. 2). Preferred methods of the invention are suitable to prepareisotopically pure B₁₈H₂₂ and mixtures of structural isomers of B₁₈H₂₂.That is, the method of the invention, provide B₁₈H₂₂ capable ofgenerating a suitable molecular ion beam for ion implantation and highpurity B₁₈H₂₂ for use in other applications.

In some aspects of the invention, a solution of B₂₀H₁₈ ²⁻ salt of theB₂₀H₁₈ ²⁻ anion is contacted with an acid ion-exchange resin and theresulting solution is of H₂B₂₀H₁₈xH₂O is concentrated by removal of themajority of solvent. Preferred solvents or solvent mixtures in whichboth the B₂₀H₁₈ ²⁻ salt and H₂B₂₀H₁₈xH₂₀ are soluble but not destroyed.These solvents and solvent mixtures may include water, alcohols,nitriles, ethers, cyclic ethers, sulfones, and the like.

In some aspects of the invention, any acidic ion-exchange resin capableof exchanging cations of a borane anion with protons are suitable foruse in the methods of synthesizing B₁₈H₂₂ provided by the invention.Preferred acidic ion-exchange resins include cross-linked,solvent-insoluble resins having a plurality of acidic functional groupscapable of exchanging a proton for the cation of the borane salt.Certain preferred acidic ion-exchange resins include aromatic orpartially aromatic polymers comprising a plurality of sulfonic acidresidues and more preferably include such aromatic or partially aromaticpolymers which are cross-linked.

B₁₈H₂₂ is produced by contacting the concentrate with a chemically inertsolvent with simultaneous water removal from the system. Although notwishing to be bound by theory, conditions conducive to removal of waterand other solvents of crystallization from the hydrated hydronium ionsalt, H₂B₂₀H₁₈xH₂O (where x is a positive real number), are alsosuitable to induce partial hydronium ion degradation. Typically,preferred degradation conditions include the use of Dean Stark trap,moisture traps, moisture scavengers or contacting the hydrated hydroniumsalt with one or more drying agents. Drying agents may include, but arenot limited to molecular sieves, phosphorus pentoxide, alumina, silica,silicates and the like, or a combination thereof. Reaction solventsshould not cause degradation to B₁₈H₂₂ or any starting materials orintermediates produced during the course of the reaction. These mayinclude, but are not limited to aromatic and arene solvents, alkanesolvents, ethers, sulfones, esters, and the like. Reaction temperaturesto promote water removal from the system range from 0° C. to about 250°C.

In a preferred aspect, the invention provides synthesizing B₁₈H₂₂ bymethods comprising the steps of:

(a) contacting the borane anion B₂₀H₁₈ ²⁻ in an acetonitrile:watersolvent mixture with an Amberlite acid ion-exchange resin to produce asolution of H₂B₂₀H₁₈xH₂O;(b) concentrating the mixture comprising H₂B₂₀H₁₈xH₂O;(c) removing water from the reaction vessel in the presence of a hottoluene (90° C. to 120° C.) through the use of a Dean Stark moisturetrap (see for instance FIG. 2);(d) separating insoluble byproducts from the reaction mixture throughfiltration;(e) removal or concentration of toluene to leave crude B₁₈H₂₂ that iscontaminated with boric acid and borates;(f) dissolution of crude B₁₈H₂₂ into hexanes and filtration ofinsolubles;(g) removal of hexanes to isolate B₁₈H₂₂

Preferred methods of the invention are suitable to provide B₁₈H₂₂capable of generating a suitable molecular ion beam for ion implantationand high purity B₁₈H₂₂ for us in other applications.

The methods of synthesis, which provide B₁₈H₂₂ in high isolated yield(>50%) and with few synthetic procedures, are suitable for use inpreparing isotopically enriched B₁₈H₂₂, e.g., the isotopic concentrationof ¹⁰B or 11B is greater than natural abundance. Preparation ofisotopically enriched, ¹⁰B or ¹¹B, B₁₈H₂₂ is practical using theinvention synthesis methods due to the limited number of syntheticsteps, mass efficiency, and high overall synthetic yield (>65% fromB₂₀H₁₈ ²⁻).

Other aspects of the invention are disclosed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a preferred process of the invention;

FIG. 2 shows use of a reaction set-up according to a preferred processof the invention.

DETAILED DESCRIPTION

FIG. 1 shows a specifically preferred process of the invention.

As discussed above, in the above methods, water may be removed from thereaction mixture by a variety of methods including e.g. through the useof moisture traps, moisture scavengers, or more drying agents such asmolecular sieves, phosphorus pentoxide, alumina, silica, silicates andthe like, or a combination thereof. A Dean-Stark trap can be preferredsuch as illustrated in FIG. 2.

In methods of the invention wherein the isotopic concentration of ¹⁰Batoms suitably may be greater than the natural abundance, e.g. whereinat least about 50% of the boron atoms present in the product B₁₈H₂₂ are¹⁰B, or wherein at least about 80% of the boron atoms present in theproduct B₁₈H₂₂ are ¹⁰B, or wherein at least about 90% of the boron atomspresent in the product B₁₈H₂₂ are ¹⁰B, or wherein at least about 95% ofthe boron atoms present in the product B₁₈H₂₂ are ¹⁰B, or wherein atleast about 99% of the boron atoms present in the product B₁₈H₂₂ are¹⁰B.

In the methods of the invention, the isotopic concentration of ¹¹B atomssuitably may be greater than the natural abundance, e.g. wherein atleast about 90% of the boron atoms present in the product B₁₈H₂₂ are¹¹B, or wherein at least about 95% of the boron atoms present in theproduct B₁₈H₂₂ are ¹¹B, or wherein at least about 99% of the boron atomspresent in the product B₁₈H₂₂ are ¹¹B.

The invention now being generally described, it will be more readilyunderstood by reference to the following example, which is includedmerely for purposes of illustration of certain aspects and embodimentsof the present invention, and are not intended to limit the invention.

EXAMPLE 1

Re-crystallized but not dried (HNEt₃)₂B₂₀H₁₈xH₂O prepared from(HNEt₃)₂B₁₀H₁₀ (333.0 g, 1.03 mol) is dissolved into 3 L of acetonitrileand 500 mL of water. The solution is then contacted with a 10 kg columnof Amberlite IR-120 acid ion exchange resin. The H₂B₂₀H₁₈xH₂O solutionis eluted with a further 3 L of acetonitrile and eluent and washingscombined. The mixture is concentrated to give a viscous yellow oil andthe mixture transferred to the flask shown in FIG. 3. 1.5 L of tolueneis added and the Dean Stark trap filled with additional toluene. Afterpurging with argon for 45 minutes, the solution is brought to refluxwith rapid stirring. Following the removal of most of the water from thereaction, hydrogen evolution significantly increases and precipitatebegins to form. When hydrogen evolution ceases, the reaction is cooledand insolubles filtered away. The toluene solution is concentrated todryness to give a light yellow powder that is extracted with 4 L ofhexanes. Any insolubles are removed by filtration. The hexane solutionis removed to leave white to off-white B₁₈H₂₂ (77.4 g, 69.1%).

EXAMPLE 2

Re-crystallized but not dried (HNEt₃)₂ ¹¹B₂₀H₁₈xH₂O prepared from(HNEt₃)₂ ¹¹B₁₀H₁₀ (5.00 g, 15.4 mmol) is dissolved into 200 mL ofacetonitrile and 25 mL of water. The solution is then contacted with a500 g column of Amberlite IR-120 acid ion exchange resin. The H₂¹¹B₂H₁₈xH₂O solution is eluted with a further 300 mL of acetonitrileand eluent and washings combined. The mixture is concentrated to give aviscous yellow oil and the mixture transferred to the flask shown inFIG. 3. 150 mL of toluene is added and the Dean Stark trap filled withadditional toluene. After purging with argon for 45 minutes, thesolution is brought to reflux with rapid stirring. Following the removalof most of the water from the reaction, hydrogen evolution significantlyincreases and precipitate begins to form. When hydrogen evolutionceases, the reaction is cooled and insolubles filtered away. The toluenesolution is concentrated to dryness to give a light yellow powder thatis extracted with 200 mL of hexanes. Any insolubles are removed byfiltration. The hexane solution is removed to leave white to off-white¹¹B₁₈H₂₂ (1.17 g, 69.0%). ¹¹B enrichment was determined to be that ofthe starting material (>98.6% ¹¹B isotopic enrichment).

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated that those skilledin the art, upon consideration of the disclosure, may make modificationsand improvements within the spirit and scope of the invention.

REFERENCES

1. Jemmis, E. D.; Balakrishnarajan, M. M.; Pancharatna, P. D.,Electronic Requirements for Macropolyhedral Boranes. Chem. Rev. 2002,102, 93-144.2. Jemmis, E. D.; Balakrishnarajan, M. M.; Pancharatna, P. D., Aunifying Electron-Counting Rule for Macropolyhedral Boranes,metallaboranes, and Metallocenes. J. Amer. Chem. Soc. 2001, 123,4313-4323.3. Pitochelli, A. R.; Hawthorne, M. F., The Preparation of a New BoronHydride B₁₈H₂₂ . J. Amer. Chem. Soc. 1962, 84, 3218.4. Hawthorne, M. F.; Pilling, R. L.; Stokely, P. F., The preparation andrearrangement of the three isomeric B₂₀H₁₈ ⁴⁻ ions. J. Am. Chem. Soc.1965, 87, 1893-1899.5. Olsen, F. P.; Vasavada, R. C.; Hawthorne, M. F., The chemistry ofn-B₁₈H₂₂ and i-B₁₈H₂₂ . J. Am. Chem. Soc. 1968, 90, (15), 3946-3951.6. Chamberland, E. L.; Muetterties, E. L., Chemistry of Boranes. XVIII.Oxidation of B₁₀H₁₀ ⁻² and its derivatives. Inorg. Chem. 1964, 3,1450-1456.

All of the patents and publications cited herein are hereby incorporatedby reference.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claim.

What is claimed is:
 1. A method of synthesizing octadecaborane (B₁₈H₂₂),the method comprising: (a) contacting the salt of borane anion B₂₀H₁₈ ²⁻with an acid to produce H₂B₂₀H₁₈xH₂O; and (b) removing water from thereaction vessel in the presence of a B₁₈H₂₂ solubilizing solvent thatremains essentially chemically inert in the system.
 2. A method ofsynthesizing octadecaborane (B₁₈H₂₂), the method comprising: (a)contacting the salt of borane anion B₂₀H₁₈ ²⁻ in solvent with an acid toproduce a solution of H₂B₂₀H₁₈xH₂O; (b) optionally concentrating themixture comprising H₂B₂₀H₁₈xH₂O; (c) removing water from the reactionvessel in the presence of a B₁₈H₂₂ solubilizing solvent that remainsessentially chemically inert in the system; and (d) optionallyseparating insoluble byproducts from the reaction mixture through (i)filtration and/or (ii) concentration of reaction solvent, dissolution ofB₁₈H₂₂ into solvent and filtration of byproducts.
 3. The method of claim2 further comprising isolating B₁₈H₂₂ through removal of solvent.
 4. Themethod of claim 2 wherein the B₂₀H₁₈ ²⁻ salt is an alkyl ammonium saltwith a cation formula of [NR¹R²R³R⁴]⁺, wherein R¹, R², and R³ areindependently selected from the group consisting of hydrogen,C₁₋₂₀alkyl, C₆₋₁₀aryl, C₇₋₁₀aralkyl, or any two of R¹, R², or R³ takenin combination form a heterocyclic ring; and R⁴ is selected fromhydrogen, C₁₋₂₀alkyl, or C₆₋₁₀aryl;
 5. The method of claim 1 or 2wherein the acid is an organic acid having a pKa of less than about 2.6. The method of claim 1 or 2 wherein the acid is an inorganic acidhaving a pKa of less than about
 2. 7. The method of claim 1 or 2 whereinthe acid is an acidic ion-exchange resin.
 8. The method of claim 7wherein the acidic ion exchange resin is an aromatic or partiallyaromatic polymer comprising a plurality of sulfonic acid residues. 9.The method of claim 7 wherein the acidic ion exchange resin is acrosslinked sulfonated polystyrene.
 10. The method of claim 1 or 2wherein the solubilizing solvent is a mixture of aqueous and non-aqueoussolvents.
 11. The method of claim 10 wherein the non-aqueous solvent isselected from the group consisting of alcohols, nitriles, ethers, andcombinations thereof.
 12. The method of claim 10 wherein the non-aqueoussolvent is methanol, ethanol, acetonitrile, tetrahydrofuran, dioxane, ora combination thereof.
 13. The method of claim 10 wherein thenon-aqueous solvent comprises between about 1% and about 99%acetonitrile by volume.
 14. The method of claim 10 wherein thenon-aqueous solvent comprises between about 80% and about 95%acetonitrile by volume.
 15. The method of claim 10 wherein thenon-aqueous solvent is acetonitrile.
 16. The method of claim 10 whereinthe solvent comprises between about 1% and 99% water by volume.
 17. Themethod of claim 10 wherein the solvent is a about a 6:1acetonitrile:water mixture by volume.
 18. The method of claim 1 or 2wherein water is removed through the use of moisture traps, moisturescavengers, or more drying agents such as molecular sieves, phosphoruspentoxide, alumina, silica, silicates and the like, or a combinationthereof,
 19. The method of claim 1 or 2 wherein water is removed throughthe use of a Dean-Stark trap.
 20. The method of claim 1 or 2 wherein thereaction solvent is selected from the group consisting of arenes,alkanes, ethers, or a combination thereof.
 21. The method of claim 20wherein the reaction solvent comprises, consists essentially of orconsists of toluene or xylene.
 22. The method of claim 1 or 2 whereinthe reaction temperature is between about 0° C. and about 200° C. 23.The method of claim 1 or 2 wherein the reaction temperature is betweenabout 50° C. and about 150° C.
 24. The method of claim 2 wherein thereaction solvent comprises, consists essentially of or consists hexanes.25. The method of claim 23 wherein the dissolution solvent is from thegroup consisting of alkanes, ethers, or a combination thereof.
 26. Themethod of claim 23 wherein the dissolution solvent comprises, consistsessentially of or consists hexanes.
 27. A method of synthesizingoctadecaborane (B₁₈H₂₂), the method comprising the steps of: (a)contacting the salt of borane anion B₂₀H₁₈ ²⁻ in solvent with acidicion-exchange resin to produce a solution of H₂B₂₀H₁₈xH₂O; (b)concentrating the mixture comprising H₂B₂₀H₁₈xH₂O; (c) removing waterfrom the reaction vessel in the presence of a B solubilizing solventthat remains essentially chemically inert in the system; (d) separatinginsoluble byproducts from the reaction mixture through (i) filtrationand/or (ii) concentration of reaction solvent, dissolution of B₁₈H₂₂into aliphatic solvent and filtration of byproducts; (e) isolation ofB₁₈H₂₂ through removal of solvent.
 28. A method of synthesizingoctadecaborane (B₁₈H₂₂), the method comprising the steps of: (a)contacting the borane anion B₂₀H₁₈ ²⁻ in a 6:1 by volumeacetonitrile:water solvent mixture with an Amberlite acid ion-exchangeresin to produce a solution of H₂B₂₀H₁₈xH₂O; (b) concentrating themixture comprising H₂B₂₀H₁₈xH₂O; (c) removing water from the reactionvessel in the presence of a hot toluene (90° C. to 120° C.) through theuse of a Dean Stark moisture trap (see FIG. 3); (d) separating insolublebyproducts from the reaction mixture through filtration; (e) removal orconcentration of toluene to leave crude B₁₈H₂₂ that is contaminated withboric acid and borates; (f) dissolution of crude B₁₈H₂₂ into hexanes andfiltration of insolubles; (g) removal of hexanes to isolate B₁₈H₂₂ 29.The method of claim 1 through 28 wherein the isotopic concentration of¹⁰B atoms is greater than the natural abundance.
 30. The method of claim29 wherein at least about 50% of the boron atoms present in the productB₁₈H₂₂ are ¹⁰B.
 31. The method of claim 29 wherein at least about 80% ofthe boron atoms present in the product B₁₈H₂₂ are ¹⁰B.
 32. The method ofclaim 29 wherein at least about 90% of the boron atoms present in theproduct B₁₈H₂₂ are ¹⁰B.
 33. The method of claim 29 wherein at leastabout 95% of the boron atoms present in the product B₁₈H₂₂ are ¹⁰B. 34.The method of claim 29 wherein at least about 99% of the boron atomspresent in the product B₁₈H₂₂ are ¹⁰B.
 35. The method of claim 1 through28 wherein the isotopic concentration of ¹¹B atoms is greater than thenatural abundance.
 36. The method of claim 35 wherein at least about 90%of the boron atoms present in the product B₁₈H₂₂ are ¹¹B.
 37. The methodof claim 35 wherein at least about 95% of the boron atoms present in theproduct B₁₈H₂₂ are ¹⁰B.
 38. The method of claim 35 wherein at leastabout 99% of the boron atoms present in the product B₁₈H₂₂ are ¹⁰B.